Biaxially stretched, blow molded bottles made of a polyethylene terephthalate resin (hereinafter referred to as a PET resin) are in wide use for beverages and the like. Patent document 1 discloses a round bottle having a cylindrical body. FIG. 10 shows a bottle described in an embodiment of this patent document 1. The bottle 101 is a biaxially stretched, blow molded round bottle made of a PET resin, i.e., a so-called PET bottle. The bottle 101 comprises a neck 102, a shoulder 103, a body 104, and a bottom 105. Six vacuum-absorbing panels 112 are disposed in the peripheral wall of the body 104 and are surrounded by step portions 111, respectively. Peripheral groove ribs 114 are disposed at upper and lower ends of the body 104.
The vacuum-absorbing panels 112 are substantially flat plates, which are deformable into a dented state toward the inside of the bottle 101 when there is a reduced pressure inside the bottle. In appearance, the bottle 101 gives no abnormal deformation, and performs a function of absorbing the reduced pressure in an inconspicuous manner (hereinafter referred to as the vacuum-absorbing function). The rigidity of the bottle is mainly borne by pillars 113 disposed between two adjacent vacuum-absorbing panels and by the peripheral groove ribs 114.